1. Field of the Invention
The present invention relates to a method and apparatus for hybrid-type high speed motion estimation for application to a moving picture encoding apparatus, and more particularly, to a method and apparatus for motion estimation combining a one-pixel greedy search (OPGS) algorithm and a hierarchical search block matching algorithm (HSBMA).
2. Description of the Related Art
In general, international video standards, such as H.261, H.263, Moving Picture Experts Group (MPEG)-1, MPEG-2, and MPEG-4, have been adopted for video services, entertainment, digital broadcasting, and portable video terminals. A video encoder for generating a bit stream according to the international video standards compresses a video signal using compression algorithms, such as discrete cosine transform (DCT), quantization, and variable length coding, and a motion estimation algorithm.
Existing motion estimation algorithms include a full-search block matching algorithm (FSBMA) and a fast search algorithm (FSA). The FSBMA first obtains differences one by one between all possible locations within a search area in the previous frame and corresponding locations in the current frame, and then finds a location having the minimum error. However, though the FSBMA is the simplest and idealistically accurate, the FSBMA requires a huge amount of calculation and therefore is not appropriate for real-time encoding.
Meanwhile, compared to the FSBMA, the FSA greatly reduces the amount of calculation at the cost of less accuracy, and is appropriate for real-time video encoders (for example, video telephones, IMT-2000 terminals, video conference systems, etc.), in which video quality is relatively less important. Examples of the FSA include a hierarchical search block matching algorithm (HSBMA), a three-step search (TSS) algorithm, a 2D logarithmic search algorithm (LSBA), and a one-pixel greedy search (OPGS).
Here, the HSBMA has high accuracy and is relatively less affected by the amount of motion, but involves a large number of calculations, and requires a memory for storing low resolution frames. Also, the HSBMA requires a large number of calculations both for a long distance motion vector and a short distance motion vector without distinction.
The OPGS algorithm can find only an effective motion vector near a central point (or a starting point), may incorrectly converge on a local minimum point, may not obtain the correct result in a complex image having complex motion, and requires a large number of calculations to find a motion vector over a long distance.
Therefore, existing motion estimation algorithms cannot utilize the already calculated results and an opportunity to reduce unnecessary calculations, because each of these algorithms is applied uniformly to all blocks, regardless of the complexity of motion, and regardless of the characteristics of a subject block. Therefore, existing motion estimation algorithms can be properly implemented in hardware, such as a very large-scale integration (VLSI) chip, but it is not efficient to implement the algorithms in a software-dedicated encoder. Also, an inexpensive price, low voltage central processing unit (CPU) cannot be used to implement the algorithms in software due to the large number of calculations.